This invention relates to a digital synchronizing arrangement for picture display device, comprising a synchronizing signal separator stage in which horizontal sync pulses are derived from a digital television signal applied to the synchronizing arrangement and comprising a horizontal synchronizing signal, and a phase-locked loop to which the horizontal sync pulses are applied for its synchronization.
Synchronizing arrangements of this type generally present the problem that the horizontal synchronizing signal can no longer be identified correctly when the input signal is distrubed and that consequently erroneous or no horizontal sync pulses are generated. This in turn results in the phase-locked loop being out of step so that a distorted picture is displayed. The same applies when there are phase jumps in the television signal.
An analog horizontal synchronizing arrangement is known from U.S. Pat. No. 3,819,859 in which a so-called window is employed to recognize the pulses included in the horizontal synchronizing signal. Dependent on the detected pulses in the horizontal synchronizing signal, this window is opened and closed again. In the time interval in which the window is opened all pulses exceeding a given threshold are evaluated as sync pulses. When the signal is distrubed, a plurality of pulses may thus be detected within one window. Moreover, problems with television signals which have phase jumps occur in this arrangement because no pulses in the horizontal synchronizing signal may then be recognized within the window. A subsequently arranged phase-locked loop will then be out of step.